The prior art for the verification of surfaces is based fundamentally on the comparison technique, by means of a feeler system which using a foreseen surface as a base points out the differences on the compared surface.
Mechanically the feeler is the organ of the copying machines which consists of a rod which slides over the surface of the piece that serves as the mold.
This feeler system is especially applicable in the reproduction of certain pieces, generally of small dimensions. It is not applicable to the verification of surfaces in large-sized pieces.